Ship hull structures deform during at-sea operations due to vibration and wave interaction. Such deformations result in relative motion between combat system elements such as radar systems, inertial navigation system (INS) sensors, and weapons systems. Since these combat system elements are often located on different parts of the ship, relative motion between them can introduce error into the targeting information provided to the weapons systems. Current Aegis combat systems do not compensate for this relative motion because the errors are deemed to be tolerable. It is expected that future combat systems, such as future Aegis Ballistic Missile Defense (BMD) baselines and CG(X), will need to compensate for relative motion between the primary radar and the INS sensors. This is because it is expected that future BMD and CG(X) will have tighter weapons system accuracy requirements, which will require relative motion compensation to meet those requirements.
Motion compensation systems are known. For example, U.S. Pat. No. 5,072,389 to Wernli et al. describes a method for compensating alignment errors in modular marine fire-control systems. The Wernli method involves the direct measurement of rotational speeds and linear accelerations at various system components to determine stabilization data for the associated equipment units. One problem with the Wernli system is that it requires the use of gyroscopes to measure rotational speeds. Such gyroscopes are expensive and require complex isolation systems to meet Navy shock requirements, resulting in substantial acquisition and maintenance costs. Thus, there is a need for a highly reliable and easy to maintain system to compensate for relative motion between combat system elements.